java练习 计算 1+1/2!+1/3!+1/4!+...1/20!=?

        double dn=0;
        double jc=1;
        for(int a=1;a<=20;a++)
        {
            jc*=a;
            dn=dn+1/jc;
        }
        System.out.println(dn);